Adherence optimization of DLC films grown on industrial application steels

Abstract

The intense need to create competitive differentiation and technological development in several industrial sectors promotes a ceaseless quest for high performance materials that promote the improvement of systems, reducing overall costs and increasing the lifetime of components and equipment. Diamond-like carbon films have attracted great industrial and scientific interest due to their differentiated mechanical and tribological properties such as low friction coefficient, excellent wear resistance, high hardness, and properties that provide a wide range of applications, as high corrosion resistance and biocompatibility. However, for an effective application of this coating, it is necessary to ensure high adhesion between film and substrate. Due to the excessive residual compressive stress which normally follows DLC films growth and the large thermal expansion coefficient difference that exists between DLC coatings and steels in general, it is difficult to deposit DLC films on substrate with high adhesion. This project aims to obtain DLC films with high adhesion on steel, through an extensive study of interfaces formation. It is intended to evaluate the physicochemical mechanisms involved in the deposition process, and to study the densification of hollow cathode plasma through changes in PECVD deposition system. It is intended to vary the growth parameters, such as pressure, bombardment energy, and deposition time, in order to obtain the best conditions of film growth. Furthermore, it is desirable to analyze the chemical bonds formed between substrate and DLC film, and to consider the different interfaces formation, such as, silicon interface, on steels with different chemical compositions and matrices. DLC films will be deposited on high industrial application steels, with different structures, compositions and properties, such as AISI 1020 steel, which is ferritic and has a ductile matrix, and AISI M2 steel, commonly used in the metal-mechanical sector for the manufacture of roughing and finishing tools. The deposition of DLC films in these materials aims to extend and enhance its applications in industry, through solving presented deficiencies, as a low corrosion resistance, for example, in addition to surfaces properties obtained with the coating. The films deposition will be performed by using the PECVD technique with pulsed DC power supply. DLC films will be analyzed by morphological, structural, electrochemical, mechanical and tribological characterization. Morphological characterization will be performed by means of scanning electron microscopy, and optical profilometry. By knowing the importance to understand the physicochemical aspects mainly related to the interface formation, the films will have their structure evaluated by Raman scattering spectroscopy, XPS (X-ray Photoelectron Spectroscopy) and SIMS (Secondary Ion Mass Spectrometry). Electrochemical characterization will be realized in order to evaluate corrosion resistance of DLC films. The adherence between film and substrate will be analyzed by scratch test and Rockwell indentation. Other tribological tests will be performed to analyze mechanical and tribological properties such as wear resistance, hardness and friction coefficient.